Many hormones and neurotransmitters communicate with their cellular targets through a mechanism which is regulated by GTP-binding proteins (G- proteins). The components of these systems, as determined from studies of the beta-adrenergic system, the traditional paradigm, are surface receptors (R), G-proteins consisting of alpha,beta and gamma subunits (G), and intracellular effectors (E). Currently, it is imperative to determine additional protein components of these systems. The eukaryotic microorganism Dictyostelium discoideum utilizes this mechanism to regulate its development, and the R's, G's and E's cloned to date are strikingly similar to their mammalian counterparts. Dictyostelium mutants which cannot develop due to defects in cell-cell communication have been isolated and will be used to detect novel components of its G-protein regulated signaling systems. Mutant cells will be transformed with a genomic expression library and observed for those cells which can now develop. The library plasmid containing the gene which "rescued" the mutant phenotype will be recovered from the rescued mutant cells and sequenced. Molecular, biochemical and genetic analyses will classify the rescuing genes as representing the mutant locus or a suppressor of the mutant phenotype. Either case will identify a protein which is involved in cell communication during development of Dictyostelium.